Phase shifting circuits



Patented 7, 1933- UNITED STATES PATENT: OFFICE BUBNICE D. BEDFORD,OFSCHENECTADY, N EW YORK, ASSIGNOR '10 GENERAL ELECTRIC COMPANY, ACORPORATION OF NEW YORK PHASE snrrrme 'cmcurrs My invention relates toelectric circuits for shifting the phase ofan alternating potentialderived from a source with respect to the potential of that source andmore 5 particularly to such electric circuits by means of which a shiftin phase of nearly 360 may be obtained by variation of the circuitelements within practical limits.

, My invention is of general application in electric control andregulating systems 'although it is particularly adapted for use inconnection with electric power converting apparatus for transmittingenergy between direct current and alternating current systems, orbetween two alternating current systems, by the use of electric valves.In such apparatus it is customary to control the transmission of powerbetween the direct current and alternating current systems by shiftingthe phase of the potentials applied-to-the control grids of the valveswith respect to the anode potentials. Various arrangements have beenprovided heretofore to effect this phase shift of the grid potentials.Static phase shifters, that is, electric circuits including'variouscombinations of resistance, reactance and capacitance, have proved to bemost satisfactory and reliability. In the static'phase shifting circuitsheretofore devised, it has been necessary to vary one of the circuitelements from zero to infinity in order to obtain a phase shift of 180,While in some instances it is desirable to obtain a phase shift of morethan 180 in order to provide the maximum flexibility in the control ofthe power converting apparatus. Obviously such a wide variation-in acircuit elementis a. practical impossibility, and even in .order tosecure a reasonable range of phase .shift it has been necessary to varythe circuit elements over extremely wide limits.

- It is an object of my invention to overcome the disadvantages abovenoted in connection with static phase shifting circuits and to providesuch a circuit in which the desired phase shift of more than 180 can ibe secured without extreme variation in the circuit elements.

means of which a shift in from the standpoint of simplicity, economy,

It is a further object of my invention to provide a staticphase-shifting circuit by I phase of nearly 3 60 can be obtained by amoderate variation of only one of the circuit elements.

According to mylinvention I provide a these circuits comprises" animpedance element or any other means for establishing a point ofmid-potential; the other circuit comprises a resist-or, a capacitor anda reactor, either the capacitor or reactor, pret erably the latter,being variable. For the most satisfactory operation of my device I havefound that it is desirable to make the impedance of the capacitorgreater than that of the resistor and the maximum impedance of thereactor, substantially twice that of the capacitor. The output potentialis taken from the mid-point of the impedance element and from theconnection between the resistorand the capacitor. In this way, thebranch of the circuit including the capacitor and the reactor may betion together with other and further objects pair of parallel electriccircuits; one of y thereof, reference is had to the followingdescription taken in connection with the accompanying drawing and itsscope will be pointed out withmore particularity in the appended claims.

Figure 1 of the accompanying drawing is a diagrammatic representation ofmy invention as applied to an electric power converting apparatusadapted to convert direct current into alternating current,

while Figs. 2 to 6, inclusive, are vector diagrams of the voltagerelations appearing in my improved phase shifting circuit to aid in theunderstanding of the invention.-

Referring to Fig. 1 of the drawing I have illustrated an electric powerconverting apparatus comprising a direct current circuit 1Ointerconnected with an alternatin current circuit 11 by a transformer 12an electric valves 13 and 14. The electric valves 13 and 14 may be ofany of the several types well-known in the art, but I prefer to usevapor electric discharge devices in which the starting of the currentthrough the device is dependent upon the otential of the control gridbut in which t e current in the device may be interrupted only byreducing theanode voltage below its critical value. A commutatingcapacitor 15 is connected between the anodes of the electric valves 13and 14 to facilitate the transfer of cm- 15 rent between them. As iswell understood by those skilled in the art, the amount of powertransmitted between thedirect current circuit 10 and the alternatingcurrent circuit 11 can be controlled by controlling the phase of thepotentials applied between the grid and the cathode of each of thevalves 13 and 14 with respect to their anode potentials. In order .tocontrol the phase of the grid potentials with respect to the anodepotentials I have shown a phase-shifting circuit comprising two parallelcircuits connected across the alternating current circuit. The first ofthese .circuits constitutes an im'edanoe'element shown as a reactor 16which serves'to provide a point of intermediate potential in thealternating current circuit, preferably a point of mid-potential. Thesecond parallel circuit .ismade up of a serially connected reactor 17,capacitor 18,

- 5 and resistor 19. The primary winding 21 of a grid transformer '22 isconnected between the mid-point of the reactor 16 and the connectionbetween the capacitor 18 and the resistor 19. The secondary winding 23of this transformer is provided with a mid- 7 tap which is connected tothe cathodes of the valves 13 and 14 through av currentlimiting resistdr24 and a negative bias battery 25, while its terminals are connected tothe grids of the electric valves'13and 14. w

The amount of power transmitted from the direct current circuit 10. tothe alternating current circuit 11 may be controlled b varying themagnitude of the reactor I; to vary the phase of the potentials appliedto the grids of the valves 13' and 14 with respect to the anodepotentials of these valves.' The manner in which this shift is elfectedmay be explained more clearly by reference to Figs. 2 to 6, inclusive,which represent the voltage vector diagrams of my improved phaseshiftingcircuit under.

' variousoperating conditions. In each of Figs. 2 to 6, inclusive'ythevector AB represents. the voltage across reactor 16, the

point O. corresponding to the potential of the potential across theresistor 19; and the so adjusted that its reactance at the frequency atwhich the. system is operating is exactly equal to that of the capacitor-18.

This condition is represented by the vector diagram of Fig. 2. Underthis condition the total impedance of this branch of the circuit is zeroand the potential a plied to the primary winding 21 of the gridtransformer is that of the left-hand portion of the reactor 16 and is,of course, in phase with the alternating potential of the circuit 11. Ifnow the inductance of the reactor 17 be decreased so that-the effectivereactancein this branch of the-circuit is capacitive, the voltageapplied to the pri-' mary winding 21 will lead the voltage of thealternating current vcircuit 11 as illustrated by the vector diagram ofFig. 3. When the inductance of the reactor 17 has been reduced to zero,the capacitor 18 is the only effective reactance in this branch of thecircuit andif this reactance is very [high .as com ared with the valueof the resistor 19, t e potential of the point 2O will approach that ofthe 'right-handten' minal of thereactor 16 very closely and thepotential applied to the primary winding 21 will lead the .potential ofthe alternating current circuit 11 by a proximately 180. Thevectordiagram of ig. 4 repre-v sents this condition. the inductance of thereactor 17 be increased sothat its reactance is greater than that of thecapacitor 18, the reactance of this branch of the circuit becomesinductive and the potential applied to the primary winding 21 will lagbehind that of the alternating current circuit 11 as illustrated by thevector diagram of Fig. 5. If the inductance of this reactor i17 beincreased to its maximum value, in which position its reactance ispreferably substantially twice that ofv the On the other hand, if

capacitor. 18, the impedance of this branch of the circuit is a ain verylarge as compared with that o the'resistor 19, the o:

tential of the point 20 will a proach t at of the right-hand terminal 0the reactor 16, and the potential applied to the primary winding 21 willlag behind that of the alternating current circuit 11 .by approximately180, This condition is represented by the vector diagram of Fig. 6.Thus, it is seen, by a variation in the value: of the reactor 17 withinpractical limits a shift in phase of 'the grid otential over nearly 360is easil obtaine The value of the resistor 19 1s preferably relativelysmall,v

being limited only'by the energy consumed when the reactance of the:reactor 17 and capacitor 18 is equal to zero.

While I have shown and described what I at present consider thepreferred embodiment of my invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madewithout departing, from my invention, and I therefore aim in theappendedclaims to cover all such changes and modifications as fallwithin the true spirit and scope of my invention. v

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:-

1. In combinationwith a source of alternating potential means forobtaining a potential variable in phase with respect thereto over arange of more than 180'electrical degrees comprising means forestablishing a point of intermediate potential of said source, atwo-part series circuit connected across said source comprisingrespectively a resistance and an inductance and capacitance one of whichis variable, and an output circuit connected between said intermediatepoint and the junction of said two-part circuit.

2. In combination with a source of alternating potential, means forobtaining a potential variable in phase with respect thereto over arange of more than 180 electrical degrees comprising an impedanceconnected across said source, a two-part series circuit connected acrosssaid source COmPIISIDg respectively a resistance and a capacitance andvarlable inductance, and an output cir- "cuit connected between anintermediate pointof said impedance and the junction of said two-partcircuit. I

3; In combination with a source of alternating potential means forobtaining a 'potential variable in phase with respect thereto overarange of more than I80 electrical degrees comprising an impedanceconnected across said source, a two-part series circuit connected acrosssaid source, the first part comprising a resistance and the second partcomprising a capacitance 7 having an impedance greater than said reofsaid source variable inducsubstantially s'istance at the frequenc and aserially 'connecte tance having an impedance twice that of thecapacitance.

.In witness whereof, I have hereunto set my hand this 26th da of Au st,1930.

- BURNI E D. B DITORD;

